In order to assist the safety of road traffic, a conventional system utilizes an ITV camera as a device for detecting road conditions, and displays a detection output from the ITV camera by means of a controller device having a display part (hereinafter mentioned as Prior Art 1). In this system, a road manager who takes charge of this controller device makes a comprehensive judgement based on the road information displayed on the display part, the road information on other areas, the weather forecast, etc. This judgement is outputted to a certain display device, which provides drivers with the road weather information or indicates safe driving signs. As the examples of conventional self-luminous road installations, use have been made of self-luminous information panels for notifying drivers of road information, LED-equipped vision guidance signs for representing a curved line shape that matches the curve on the road. The luminous part in these self-luminous road installations can be regulated at a fixed brightness, or two-stage brightness control can be applied to adjust the brightness for the day and the night, respectively.
As disclosed in Japanese Patent Application Laid-open No. H9-128688, a system for assisting safe road travel (hereinafter mentioned as Prior Art 2) comprises obstruction detecting means which includes a visibility meter and an obstruction detection radar for detecting the road driving environment, and displaying/warning means which is controlled in accordance with the output from the obstruction detecting means. These means are combined as an obstruction detecting/warning device, which is serially installed along the central reserve or a side of a road.
This system has the displaying/warning means integrated into the obstruction detecting/warning device, which is serially located along the central reserve or a side of a road. The display modes of the displaying/warning means include sound, text display, indication light (in regard to color, brightness and flash interval) and the like, and these modes can be applied singly or in combination.
As mentioned above, Prior Art 1 uses an ITV camera as the device for detecting road conditions. The ITV camera, however, is very expensive and should be mounted on a large gatepost or a giant system. Besides, in order to provide detailed information to drivers, a number of ITV cameras should be installed at required locations. Hence, it is practically impossible to place so many ITV cameras in the above manner. In another respect, since this system depends on a road manager for a comprehensive judgement, the system requires much time for such judgement and fails to give real-time information. What is worse, this self-luminous road installation is controlled to give a light at a fixed brightness. Accordingly, when visibility drops under bad weather conditions (e.g. fog, snow), the luminous brightness is seriously degraded from the viewpoint of drivers. As a consequence, the signing function as the road sign device is impaired. This problem may be solved by setting the luminous brightness of a sign, based on the low visibility situation under poor weather conditions. However, drivers find such illumination too bright in the night and feel awkward even during the day. Thus, this attempt is rather dangerous to the drivers, only to create another problem. Besides, when the level of luminous brightness is intensified, the structure consumes a greater amount of electric power and, therefore, is uneconomical.
As for Prior Art 2, the system does not rely on the centralized management by a road manager, and it assists drivers' safe driving by furnishing local or fixed individual information. In this case, it is difficult to grasp foggy, snowy or other conditions in a wide area properly, or to assist safe driving in compliance with the changing weather conditions in a particular area or the conditions across some areas. Besides, the displaying/warning means provides a single type of information merely by issuing a warning in response to obstructions on the road. More disappointingly, despite the fact that the visual perceptibility is adversely affected under a low visibility condition, the information is displayed without any consideration.
The present invention has been made for the purpose of solving these problems. The first object is to provide a road traffic weather-monitoring system which properly grasps foggy, snowy and other conditions in a wide area and which allows a road manager and others, in response to such conditions, to issue real-time weather information to drivers, thereby contributing to safe vehicle travel.
The second object is to provide a self-luminous road sign system which prevents degradation of the luminous brightness of a self-luminous road installation and improves its visual perceptibility even in a poor visibility situation, and which ensures reliable visual guidance.